The present invention relates to a focused ion beam (FIB) apparatus using a liquid metal ion source to perform, for example, cutting of a specimen and more particularly, to an FIB apparatus provided with an aperture having a less adverse influence upon the liquid metal ion source and a structure of the aperture used for the FIB apparatus.
In the FIB apparatus, a liquid metal ion source is highly bright and reduced in source size and is therefore used in general as the ion source. In order to use the liquid metal ion source stably, a liquid metal of the ion source must be kept to be clean and for this end, formation of a gallium oxide film, surface contamination due to, for example, a sputter re-deposited film and intrusion of impurities must be suppressed to a minimum.
Conventionally, with a view to attaining the object as above and protecting an aperture per se by taking advantage of the fluidity of liquid metal, a method of covering the aperture with a liquid metal has been proposed in, for example, Japanese Patent No. 3190395 (Patent Document 1) or JP-A-5-159730 (Patent Document 2). More particularly, a liquid metal used as an ion source material is held by coating it on the surface of an aperture or by permeating it into a sintered body so that contamination of a liquid metal ion source due to sputter re-deposition of a material of the aperture and damage of the aperture per se may be prevented.
Especially, in an aperture disposed immediately beneath an ion source, a material constituting the aperture greatly affects the liquid metal ion source by its re-deposition on the source. Therefore, as described in JP-A-2001-160369 (Patent Document 3), an aperture having a dish-like vessel in which a liquid metal is carried or pooled is used to prevent instability attributable to re-deposition.
In the technologies described in the Patent Documents 1 and 2, however, a liquid metal is in essence impregnated in a porous material and there is a possibility that during use, the porous material is sputtered and the ion source is contaminated, giving rise to a fear that the ion source becomes unstable. In the technology described in the Patent Document 3, the liquid metal is carried on the dish-like vessel and as compared to the techniques described in the Patent Documents 1 and 2, the amount of an ion beam impinging upon a portion other than the liquid metal can be decreased. But, in a hole of the dish-like vessel through which the ion beam passes, the ion beam is irradiated on a material other than the liquid metal and there is a possibility that the material sputtered from the hole portion will contaminate the liquid metal ion source. Further, since a portion of dish-like vessel at which the liquid metal is pooled is flat, the liquid metal coheres in an island pattern on the bottom of the dish-like vessel as the quantity of liquid metal decreases and there is also a possibility that the liquid metal is lost around the hole of disk-like vessel through which the ion beam passes.